1. Field of the Invention
The present invention relates to a spinning machine, especially to a drawing frame which is one kind of spinning machines and it is utilized as a machine for carding raw materials such as wool, and the like in the form of one or plural slivers and for preparing another new sliver or slivers by carrying out the draft thereof.
2. Description of the Related Art
Conventionally, when spinning a raw material for yarn, such as wool, the entangled or twisted wool is firstly rinsed and then dried. The wool thus dried is unravelled by a machine called a carding machine and it is made into a batch of fibers called a sliver. Then, a sliver or slivers are put together and are drafted while carding the sliver or slivers by a drawing frame having a unit for carding called a gill box and then a new sliver is spin thereby.
Furthermore, the sliver thus prepared is again applied to the drawing frame and the carding and drafting processes are repeated. In this case, if necessary, the sliver is glossed, and string of yarn is finally formed.
One example of the structure of the drawing frame for carding and drafting, according to the prior art, is shown in FIG. 1. The drawing frame comprises a pair of feed rollers 1, a pair of front rollers 2, a plurality of rotating combs 3a as shown in FIG. 2 or a plurality of laterally moving combs 3b as shown in FIG. 3, which are arranged in a gill box 3 located between the feed rollers 1 and the front rollers 2 for carding. In this case, the speed for carding a sliver 4 within the gill box 3 is equal to to the feeding speed of the pair of feed rollers 1 for feeding the sliver 4 to the gill box 3. On the other hand, the feeding speed of the pair of front rollers 2 which feed the sliver 4, which is discharged from the gill box 3, is determined in accordance with a predetermined draft rate. For instance, the ratio of the carding speed in gill box 3 and rotational speed of the pair of front rollers 2, which is same as the feeding speed of the pair of feed rollers 1, is 5:1, if the draft rate is 5.
Accordingly, supposing that a sliver 4 having the weight of 50 g per meter is passed by the drawing frame 9, it is to be drafted into a sliver having the weight of 10 g per meter. Moreover, the drawing frame further comprises an unevenness detector 5 for detecting unevenness of the sliver 4, which is provided upstream of, and close to, the pair of feed rollers 1 and a mechanical memory 6 for storing information about unevenness detected by the detector 5.
The drawing frame further includes a drive motor M for driving the pair of feed rollers 1, the pair of front rollers 2 and the combs 3a or 3b in the gill box 3 through gears 7 and pulleys 8. When operating the drawing frame, the pair of feed rollers 1, the pair of front rollers 2 and the combs 3a or 3b in the gill box 3 start rotating simultaneously, and they are accelerated to a predetermined speed, while maintaining a constant draft rate so as to prevent the sliver 4 from being cut, or prevent the sliver from being jammed within the gill box 3. Moreover, when stopping the drawing frame, the feed rollers, the front rollers, and the combs are decelerated until they are stopped simultaneously, while the draft rate is maintained constant.
It is necessary for the draft rate of the drawing frame 9 to be changed in accordance with the nature of raw materials used, products to be made, and process, etc. Accordingly, the draft rate is normally adjustable by interval of 0.15 within the draft rate of 1 to 10. Conventionally, in this case, since about twenty gears had to be displaced, much time was required for changing gears, and the efficiency of the work was not necessarily good. In addition, it was difficult in practice to adjust the draft rate by the interval of 0.15 within the predetermined draft range by use of only gears 7 and the pulleys 8. Moreover, in order to correct unevenness the drawing frame 9 according to the prior art comprises an expensive stepless speed change gear 10 between the drive motor and that pair of front rollers 2 so as to carry out a fine adjustment thereof. Information relative to an uneven part of the sliver 4 which has been stored in the mechanical memory 6 is converted into a signal to change the transmission ratio or speed change ratio of the stepless change gear 10 via a hydraulic actuator 12 supplied with pressure oil through a controll valve 11, when the unevenness reaches the front rollers 2.
However, since the mechanical memory 6 as shown in FIG. 4 as well as the stepless speed change gear 10 is used in the drawing frame 9 according to the prior art, the allowance range of the adjustment of thickness will be within .+-.25%; therefore, the response characteristic of the machine is low. For instance, in a high speed drawing frame for carding, it is difficult to correct an unevenness of the sliver 4 having an length of less than 1 meter, and there is a drawback such as the normal portion downstream of the uneven part of sliver 4 is made irregular, due to the delay in control.
This is because a number of pins 6c in the mechanical memory 6 are provided at circular guides 6B which rotate together with a rotational shaft 6A which also rotates in synchronization with the pair of feed rollers 1, in such a manner that the number of pins c slide in the direction of a shaft paralleled with the rotational shaft 6A, and a lever 6D for pushing the pins is moved left and right in FIG. 4 by the operation of the unevenness detector 5. As a result, the pins 6c are slid and deviated, thus memorizing the unevenness of the sliver 4. When the deviated portion is moved or travelled to a predetermined position in accordance with rotation of the rotational shaft 6A, the degree of the slid deviation is picked up by a pin follower 6E, and the control valve 11 is operated thereby. Some propagation delay time inevitably occurs when signals are transmitted from the mechanical memory 6 to the control valve 11, and then to the hydraulic actuator 12 and finally to the stepless speed change gear 10 with the construction according to the prior art. This propagation delay time results in the delay in response in the high speed drawing frame 9 according to the prior art.